This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A329890 #7 Aug 18 2024 14:46:27
%S A329890 1,3,4,16,8,72,24,304,160,944,624,6576,-544,14336,16384,72544,19616,
%T A329890 342528,50688,1475584,466176,3443712,2657376,29486880,-3340288,
%U A329890 54808448,65971360,306781024,77647680,1475408064,132153344,5157119680,3054411072,12548176896,13343981568,130039259136,-28235160128,228451400256,269821673472
%N A329890 a(1) = 1; for n > 1, a(n) = sigma((2^n)-1) - sigma((2^(n-1))-1), where sigma is A000203, the sum of divisors.
%H A329890 <a href="/index/Si#SIGMAN">Index entries for sequences related to sigma(n)</a>
%F A329890 a(1) = 1; and for n > 1, a(n) = A075708(n) - A075708(n-1).
%t A329890 Join[{1},Table[DivisorSigma[1,2^n-1]-DivisorSigma[1,2^(n-1)-1],{n,2,40}]] (* _Harvey P. Dale_, Aug 18 2024 *)
%o A329890 (PARI) A329890(n) = if(1==n,1,sigma((2^n)-1)-sigma((2^(n-1))-1));
%Y A329890 From second term onwards, the first differences of A075708.
%Y A329890 Cf. A000203, A329637, A329891, A329892.
%K A329890 sign
%O A329890 1,2
%A A329890 _Antti Karttunen_, Dec 08 2019